The average electron donor properties of Cu+ ions in CuZSM-5 were found to be stronger than in CuMCM-41. This was evidenced by IR studies of CO, N-2 and NO adsorption. The stronger electron donor properties of Cu+ the stronger it activates adsorbed molecules by pi-back donation. This is why Cu+ ions in CuZSM-5 are more active in "deNOx" reaction than in CuMCM-41. IR studies of CO and N-2 desorption showed that Cu+ ions in both CuZSM-5 and CuMCM-41 were heterogeneous and the Cu+ sites of various electron donor properties were present. Quantumchemical DFT calculations showed that the electron donor properties of Cu+ (electrical charge and energy of HOMO) depend on the location of Cu+ in zeolites. Cu+ ions in 6 sites (of higher number of oxygen atoms surrounding the cation) are stronger electron donor than Cu+ ions in beta sites. The calculations evidenced also that Cu+ in alpha sites activate stronger NO molecules than in beta sites. (C) 2004 Elsevier B.V. All rights reserved.